A sign hangs outside the grounds of the former Rocky Flats nuclear weapons production facility on May 29, 2014.

A new survey on the health of people who live or lived near the former Rocky Flats nuclear weapons plant shows enough worrisome results to warrant further study, the nurse overseeing the survey said Friday.

Carol Jensen, a nurse and a professor at Metropolitan State University of Denver, said survey respondents reported unexpectedly large numbers of cases of thyroid cancer and rare cancers. But Jensen cautioned that the survey is not statistically rigorous, and that people who are ill likely responded more readily to the survey than those who aren’t. There is no way currently to determine whether those cancers identified occurred at higher rates in people who lived near Rocky Flats than they do in the general population, she said.

“We’ve identified some patterns that do warrant further investigation,” she told a standing-room-only crowd in Arvada at the first of two public meetings Friday, at which the initial survey results were announced. “That’s the most I can tell you at this point.”

The survey was launched in May in cooperation with the Rocky Flats Downwinders citizen group. The survey, which is still ongoing, seeks to collect health information from people who lived between 1952 and 1992 in an area bounded by Colorado 128 and 120th Avenue on the north, Interstate 25 on the east, Interstate 70 on the south and Colorado 93 on the west.

More than 1,700 people responded, more than 800 of whom reported cases of cancer. Jensen said thyroid cancer — the ninth-most-common type of cancer in Colorado, according to the Centers for Disease Control and Prevention — was the second-most-common kind reported by survey respondents. Jensen said researchers will next collect oral histories from respondents to validate the information they provided and also learn more.

Rocky Flats, located 16 miles northwest of downtown Denver, produced the plutonium triggers that went into some of the most destructive nuclear bombs ever built. Operating in secrecy, Rocky Flats also quietly sowed contamination, including two plutonium fires in the 1950s and 1960s that sent plumes across the northwest metro area and storage leaks that dripped radioactivity into the soil.

The state and federal governments undertook a cleanup effort on the site, and the Rocky Flats National Wildlife Refuge — a 5,000-acre expanse that excludes the core 1,300 acres where the plant operated — is scheduled to open to the public in 2018.

But the original study didn’t look specifically at thyroid cancer, and the database may not be able to identify cases of people who once lived near Rocky Flats but moved away before being stricken with cancer. Jensen said the new survey is the first to directly ask community members about illnesses that may have been caused by Rocky Flats contamination.

At Friday’s meeting, one attendee after another raised their hands during a question-and-answer period to recount stories of cancers or other illness that have affected their families.

“That’s one of the problems with disease and environment,” she said to them. “It’s very hard to prove causation.”

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